At least some known currently used odor control technologies are prepared by chemically depositing transition metal layers onto the surface of silica nano-particles. For instance, U.S. Patent Pub. No, 2005/0084438 to Do, et al., describes modifying the surface of silica particles with a transition metal so that the silica particles are bonded to the transition metal through a covalent or coordinate bond. Further, U.S. Patent Pub. No. 2006/0008442 to MacDonald, et al. describes modified nano-particles that have active sites that bind various gases and/or odorous compounds, thereby removing these compounds from a medium such as air or water. The metal ions are absorbed onto the surface of the nano-particle and bound strongly to the surface. These modified nano-particles may be applied to nonwoven webs to provide odor removing articles for industrial and consumer use. Although these modified nano-particles are useful, current procedures for forming these nano-particles have multiple problems, which can waste time, energy, and money for manufacturers of these modified nano-particles.
Specifically, synthesis of this technology is sensitive to reagent concentration, as aggregation and gelation in the reaction suspension may be observed at silica nano-particle concentrations above 4% (wt/wt). With this constraint, manufacturing and processing of the technology at the production scale entails higher costs due to more energy expensed to remove higher volumes of solvent. Additionally, more substrate material is needed in order to incorporate higher loading of technology into the product for increased odor removal efficacy. Particle agglomeration, also referred to herein as gelation, may be driven by a strong ionic strength nature in the reaction media due to the chemicals in that media.
Further, modified nano-particles formed by a stirred suspension of silica particles and copper salts with a base that is slowly added results in the active metal complex being formed on the surface of the silica in discrete zones or nodes. It has been discovered that the modified nano-particles formed by this method are capable of converting, for example, thiols (mercaptans) odors into disulphides. The human nose is particularly sensitive to these odors and can detect the presence of thiol odors down to part-per-billion (ppb). The human nose's ability to detect disulphides, however, is significantly less, in fact around tens of parts-per-million (ppm). Thus, the modified nano-particles may convert the malodor into a compound that can only be detected at significantly higher levels and therefore effectively converts the odor into something the human nose cannot detect. The modified nano-particles could perform this catalytic conversion continuously for an extended period of time.
Once the modified nano-particles are formed, three major mechanisms are involved in remediation of odor compounds: (1) physical adsorption; (2) catalysis; and (3) chemical absorption. Physical adsorption is the main pathway by which activated carbon material function. The advantages of this mechanism include rate and capacity effectiveness, however, the adsorption can be reversed at changes in temperature or humidity. Catalysis involves the conversion of an odor compound to another compound. Ideally, the converted compound should be heavier and posses a higher boiling point and/or a lower vapor pressure, thus not allowing it to be re-emitted into the atmosphere. This is not guaranteed or predictable, however, and may lead to disadvantages compared to something that is more irreversible. Chemical absorption involves the chemical binding of the odor compound to the odor removal compound. Typically, the binding is irreversible when subject to physical challenges such as temperature and humidity. It has been shown that odorous compounds are removed from metal-modified silica nano-particles via the catalytic mechanism when the metal-modified silica nano-particles are prepared without the presence of ultrasound energy.
Based on the foregoing, there is a need in the art for a method of preparing metal-modified silica particles by ultrasonically mixing a first and second formulation. Furthermore, it would be advantageous if the system could be configured to enhance the cavitation mechanism of the ultrasonics, thereby decreasing particle agglomeration and changing the mechanism by which odorous compounds will be removed during use of the metal-modified particles.